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Sept. 21, 2011 -- Eight people have died in the ongoing outbreak of listeria food poisoning from Colorado cantaloupes.

There have been four deaths in New Mexico, two in Colorado, one in Maryland, and one in Oklahoma.

The CDC now has 55 reported illnesses from 14 states:

California (1 case)

Colorado (14)

Illinois (1)

Indiana (1)

Maryland (1)

Montana (1)

Nebraska (4)

New Mexico (10)

Oklahoma (8)

Texas (9)

Virginia (1)

West Virginia (1)

Wisconsin (2)

Wyoming (1)

Listeria cases in several other states may also be linked to the outbreak. These cases are still being investigated. Illnesses that began after Aug. 28 may not yet have been reported.

All illnesses began on or after Aug. 4. In all cases for which medical records are available, the patient was hospitalized.

Listeriosis, caused by Listeria monocytogenes bacteria, can cause lethal or disabling encephalitis and meningitis, usually in older people or those with weakened immune systems. Listeria can also cause fatal fetal infections in pregnant women.

Four distinct strains of listeria are causing the current outbreak. Strains linked to the outbreak have been cultured from Jensen Farms' Rocky Ford brand cantaloupe from a Denver-area store and from equipment and cantaloupe at the Jensen Farms packing plant.

No other farms, even in the Colorado's Rocky Ford growing region, have been linked to the outbreak.

Jensen Farms has recalled all cantaloupes shipped from July 29 through Sept. 10 to at least 17 states. Further distribution may have occurred.

If you encounter unlabeled cantaloupes, you should ask your grocer where it came from.

If you have one of the recalled cantaloupes, be sure to dispose of it in a closed plastic bag in a sealed trash can to prevent people or animals from eating it.

If you've eaten some of a recalled cantaloupe and have not become sick, do not assume the cantaloupe is safe. Dispose of it immediately.

The FDA warns people not to try to wash bacteria from the recalled cantaloupes, as both the inside and outside of the melons may be contaminated.

Listeria monocytogenes bacteria are commonly found in the soil, where they eat dead plant matter. When consumed, the bacteria change their nature and become able to enter cells. Unless controlled by the immune system, they can escape the gut and enter the bloodstream.

Listeriosis Symptoms

Although listeriosis is a food-borne illness, disease with symptoms usually means the bacteria have escaped the digestive tract and are spreading throughout the body. Listeriosis often results in fatal meningitis or encephalitis.

Listeriosis usually begins with diarrhea or other intestinal symptoms. Patients soon develop fever and muscle aches. What happens next depends on a person's risk factors:

While pregnant women usually get a mild flu-like illness, listeria infection can cause miscarriage, stillbirth, premature delivery, or fatal infection of the newborn.

Other people at high risk may develop a headache, stiff neck, mental confusion, loss of balance, and convulsions.

Foods typically linked to listeriosis are deli meats, hot dogs, and soft cheeses made with unpasteurized milk. Produce is less often linked to outbreaks, although listeria occurs in soil and water. Listeria is killed by cooking, but can grow and multiply in refrigerators.

How to Avoid Listeria

As contaminated cantaloupes may still be in grocery stores or in people's homes, the CDC has issued this advice:

People at high risk for listeriosis, including older adults, people with weakened immune systems, and pregnant women, should not eat cantaloupes marketed as coming from the Rocky Ford region of Colorado.

People who have cantaloupes in their homes can check the label or inquire at the store where they purchased it to determine if the fruit was marketed as coming from the Rocky Ford region of Colorado.

Listeriosis primarily affects older adults, people with weakened immune systems, pregnant women, and newborns. People who think they might have become ill from eating contaminated cantaloupes should consult their doctor immediately.

Cantaloupes marketed as coming from the Rocky Ford region should be disposed of in a closed plastic bag placed in a sealed trash can. This will prevent people or animals from eating them.

As other foods besides cantaloupes can carry listeria, the CDC recommends these general steps to avoid listeriosis:

Rinse raw produce, such as fruits and vegetables, thoroughly under running tap water before eating. Dry the produce with a clean cloth or paper towel before cutting it up.

Thoroughly cook raw meat and poultry.

Heat hot dogs, deli meats, and cold cuts until they are steaming hot just before serving.

Do not drink raw (unpasteurized) milk and do not eat fresh soft cheeses that have unpasteurized milk in them, especially Mexican-style cheeses like queso fresco.

Be sure that your refrigerator is at or below 40 degrees F and your freezer is at or below 0 degrees F by using a refrigerator thermometer.